<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      div {
        width: 600px;
        margin: 100px auto;
      }

      .message {
        display: inline-block;
        font-size: 12px;
        color: #999;
        background: url(images/mess.png) no-repeat left center;
        padding-left: 20px;
      }

      .wrong {
        color: red;
        background-image: url(images/wrong.png);
      }

      .right {
        color: green;
        background-image: url(images/right.png);
      }
    </style>
  </head>
  <body>
    <div class="register">
      <input type="password" class="ipt" />
      <p class="message">请输入6~16位密码</p>
    </div>
    <script>
      var ipt = document.querySelector(".ipt");
      var p = document.querySelector("p");
      ipt.onblur = function () {
        if (ipt.value.length < 6 || ipt.value.length > 16) {
          p.innerHTML = "输入有误";
          p.className = " message wrong";
        } else {
          p.innerHTML = "输入正确";
          p.className = " message right";
        }
      };
    </script>
  </body>
</html>
